[tests] update periodic_timer tests to reduce flakiness.

These tests check for lowerbounds on the time it took to fire an
event. Unfortunately, browsers may complete events ahead of time.
This has caused these tests to be flaky in dart2js and ddc [1]

In a local experiment, we've seen timers complete +-15ms from
the expected time. Most often they are around +-5ms, but those more
extreme cases do happen. Recent flakiness logs show some good samples:
* off by 1ms: [2] and [3]
* off by 4ms: [4]
* off by 13ms: [5]

This CL makes two adjustments to reduce flakiness:
* account for the fact that timers may complete early (checking that
  they are >= than the expected timeout - 40ms)
* increase intervals to 50ms in order to prevent overlap between two
  events in the worse scenario that both happen on the extreme variances
  (+15ms and -15ms respectively).

[1]: https://dart-current-results.web.app/#/filter=lib/async/periodic_timer,dart2js,ddc&showAll
[2]: https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket/8766776511992750881/+/u/test_results/ignored_flaky_test_failure_logs
[3]: https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket/8766798962026535617/+/u/test_results/ignored_flaky_test_failure_logs
[4]: https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket/8767378609439308945/+/u/test_results/ignored_flaky_test_failure_logs
[5]: https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket/8767357850408867553/+/u/test_results/ignored_flaky_test_failure_logs

Change-Id: Ib46d6f33f5c2b1458f393e8b4c75c84453e73024
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/331210
Reviewed-by: Stephen Adams <sra@google.com>
Commit-Queue: Sigmund Cherem <sigmund@google.com>
3 files changed
tree: 42e20a52a59c14f94572b33499d8d5b637a45995
  1. .dart_tool/
  2. .github/
  3. benchmarks/
  4. build/
  5. docs/
  6. pkg/
  7. runtime/
  8. samples/
  9. sdk/
  10. tests/
  11. third_party/
  12. tools/
  13. utils/
  14. .clang-format
  15. .gitattributes
  16. .gitconfig
  17. .gitignore
  18. .gn
  19. .mailmap
  20. .style.yapf
  21. .vpython
  22. AUTHORS
  23. BUILD.gn
  24. CHANGELOG.md
  25. codereview.settings
  26. CONTRIBUTING.md
  27. DEPS
  28. LICENSE
  29. OWNERS
  30. PATENT_GRANT
  31. PRESUBMIT.py
  32. README.dart-sdk
  33. README.md
  34. sdk.code-workspace
  35. sdk_args.gni
  36. SECURITY.md
  37. WATCHLISTS
README.md

Dart

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